Structure and Bonding Investigation of Plutonium Peroxocarbonate Complexes Using Cerium Surrogates and Electronic Structure Modeling.

Herein, we report the synthesis and structural characterization of K[(CO)Pu](μ-η-η-O)·12HO. This is the second Pu-containing addition to the previously studied alkali-metal peroxocarbonate series M[(CO)A](μ-η-η-O)·xHO (M = alkali metal; A = Ce or Pu; x = 8, 10, 12, or 18), for which only the M = Na analogue has been previously reported when A = Pu. The previously reported crystal structure for Na[(CO)Pu](μ-η-η-O)·12HO is not isomorphous with its known Ce analogue. However, a new synthetic route to these M[(CO)A](μ-η-η-O)·12HO complexes, described below, has produced crystals of Na[(CO)Ce](μ-η-η-O)·12HO that are isomorphous with the previously reported Pu analogue. Via this synthetic method, the M = Na, K, Rb, and Cs salts of M[(CO)Ce](μ-η-η-O)·xHO have also been synthesized for a systematic structural comparison with each other and the available Pu analogues using single-crystal X-ray diffraction, Raman spectroscopy, and density functional theory calculations. The Ce salts, in particular, demonstrate subtle differences in the peroxide bond lengths, which correlate with Raman shifts for the peroxide O-O stretch (O = O atoms of the peroxide bridges) with each of the cations studied: Na [1.492(3) Å/847 cm], Rb [1.471(1) Å/854 cm], Cs [1.474(1) Å/859 cm], and K [1.468(6) Å/870 cm]. The trends observed in the O-O bond distances appear to relate to supermolecular interactions between the neighboring cations.